<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        p{
            color:red;
        }

        /*见名知意，多个单词用-链接*/
        .red{
            color:blue;
        }

        .size{
            font-size: 50px;
        }
    </style>
</head>
<body>
    <p>吃饭</p>
    <p>睡觉</p>
    <div class="red size">div  标签</div>
</body>
</html>